Sunflower is not a flower. Explain

Sunflower is not a flower. Explain.

Sunflower is an inflorescence called capitulum or racemose head. It has a flat disc-shaped peduncle called receptacle. It hears an involucre of bracts on the periphery and two types of small sessile flowers called florets. The flower is arranged centripetally with youngest towards the periphery. There are ray florets which are sterile female flowers of ligulate type on the outside. The rest of the flowers are disc florets which are fertile bisexual flowers of tubular type.